X-Git-Url: https://thelambdalab.xyz/gitweb/index.cgi?a=blobdiff_plain;f=scheme.4th;h=5ad37c6c98cd09ecf41b2235b80731a85a02e62b;hb=2ab189727b2f1502367dae83dfaf931e3eab1684;hp=65c64a895b702796b7c36343d5e6a0182be2d023;hpb=ab2c14cdd02f93d17f8784e790415de0e6d7b996;p=scheme.forth.jl.git

diff --git a/scheme.4th b/scheme.4th
index 65c64a8..5ad37c6 100644
--- a/scheme.4th
+++ b/scheme.4th
@@ -5,151 +5,213 @@ scheme definitions
 
 include term-colours.4th
 
-\ Cons cell memory
-1000 constant memsize
-create car memsize allot
-create cdr memsize allot
-create types memsize allot
+0 constant number-type
+1 constant boolean-type
+: istype? ( obj -- obj b )
+    over = ;
 
-0 constant symbol-type
-1 constant int-type
-2 constant list-type
-3 constant bool-type
+\ ---- Read ----
 
-variable nextfree
-0 nextfree !
-
-: stack
-    create here 1+ , allot ;
-
-
-: push ( st v -- )
-    over @ !
-    1 swap +!
-;
+variable parse-idx
+variable dummy-parse-idx
 
-: pop ( st -- v )
-    dup @       ( s0 sp )
-    1-          ( so sp' )
+: store-parse-idx
+    parse-idx @ dummy-parse-idx !  ;
 
-    2dup = abort" Stack underflow."
-    
-    dup @       ( s0 sp' v )
-    -rot swap   ( v sp' s0 )
-    !
-;
+: restore-parse-idx
+    dummy-parse-idx @ parse-idx !  ;
 
-100 stack parse-stack 
-variable parse-idx
 variable parse-str
 
-
-: inc-parse-idx parse-idx +! ;
-: dec-parse-idx parse-idx -! ;
-
-: ?charavailable ( -- bool )
+: charavailable? ( -- bool )
     parse-str @ @ parse-idx @ >
 ;
 
 : nextchar ( -- char )
-    ?charavailable if
+    charavailable? if
         parse-str @ 1+ parse-idx @ + @
     else
         0
     then
 ;
 
-: ?whitespace ( -- bool )
+: whitespace? ( -- bool )
     nextchar BL = 
     nextchar '\n' = or
 ;
 
-: ?delim ( -- bool )
-    ?whitespace
+: delim? ( -- bool )
+    whitespace?
     nextchar [char] ( = or
     nextchar [char] ) = or
 ;
 
 : eatspaces
     begin
-        ?whitespace
+        whitespace?
     while
             1 parse-idx +!
     repeat
 ;
 
-: parsebool
+: digit? ( -- bool )
+    nextchar [char] 0 >=
+    nextchar [char] 9 <=
+    and ;
 
-    nextchar emit cr
-    trace
+: minus? ( -- bool )
+    nextchar [char] - = ;
 
-    false
-    nextchar [char] # <> if exit then
+: number? ( -- bool )
+    digit? minus? or false = if
+        false
+        exit
+    then
 
-    1 inc-parse-idx
+    store-parse-idx
+    1 parse-idx +!
 
-    nextchar dup [char] t = swap [char] f = or
-    not if
-        1 dec-parse-idx
-        exit
+    begin digit? while
+        1 parse-idx +!
+    repeat
+
+    delim? charavailable? false = or if
+        restore-parse-idx
+        true
+    else
+        restore-parse-idx
+        false
     then
+;
 
-    1 inc-parse-idx
+: boolean? ( -- bool )
+    nextchar [char] # <> if false exit then
 
-    ?delim not if
-        2 dec-parse-idx
-        exit
+    1 parse-idx +!
+
+    nextchar [char] t <>
+    nextchar [char] f <>
+    and if 1 parse-idx -! false exit then
+
+    1 parse-idx -!
+    true
+;
+
+: readnum ( -- num-atom )
+    minus? dup if
+        1 parse-idx +!
+    then
+
+    0
+
+    begin digit? while
+        10 * nextchar [char] 0 - +
+        1 parse-idx +!
+    repeat
+
+    swap if negate then
+
+    number-type
+;
+
+: readbool ( -- bool-atom )
+    1 parse-idx +!
+    
+    nextchar [char] f = if
+        false
+    else
+        true
     then
+
+    boolean-type
 ;
 
-: parsetoken
+\ Parse a counted string into a scheme expression
+: read ( -- obj )
 
     eatspaces
 
-    \ Parens
-
-    nextchar [char] ( = if
-        \ todo
+    number? if
+        readnum
         exit
     then
 
-    nextchar [char] ) = if
-        \ todo
+    boolean? if
+        readbool
         exit
     then
 
-    parsebool if
+    bold fg red ." Error parsing string starting at character '"
+    nextchar emit
+    ." '. Aborting." reset-term cr
+    abort
+;
+
+\ ---- Eval ----
+
+: self-evaluating? ( obj -- obj bool )
+    number-type istype? if true exit then
+    boolean-type istype? if true exit then
+    false ;
+
+: eval
+    self-evaluating? if
         exit
-    exit
+    then
+
+    bold fg red ." Error evaluating expression - unrecognized type. Aborting." reset-term cr
+    abort
 ;
 
-\ Parse a counted string into a scheme expression
-: parseexp ( straddr n -- exp )
-    0 parse-idx !
+\ ---- Print ----
 
-    begin
-        parsetoken
-    nextchar 0 =
-    until
+: printnum ( numobj -- ) drop . ;
+: printbool ( numobj -- )
+    drop if
+        ." #t"
+    else
+        ." #f"
+    then
+;
+
+: print ( obj -- )
+    ." ; "
+    number-type istype? if ." => " printnum exit then
+    boolean-type istype? if ." => " printbool exit then
 ;
 
 \ ---- REPL ----
 
 create repl-buffer 161 allot
+repl-buffer parse-str !
 
-: repl
-    repl-buffer parse-str !
-
-    cr
+: getline
+    repl-buffer 1+ 160 expect span @ repl-buffer ! ;
 
-    begin
-        bold fg green ." => " reset-term
+: eof?
+    repl-buffer @ 0= if false exit then
+    repl-buffer 1+ @ 4 <> if false exit then
+    true ;
 
-        repl-buffer 1+ 160 expect cr
-        span @ repl-buffer !
+: repl
+    cr ." Welcome to scheme.forth.jl!" cr
+       ." Use Ctrl-D to exit." cr
 
-        parseexp
-        \ eval
+    begin
+        cr bold fg green ." > " reset-term
+        getline
+
+        eof? if
+            bold fg blue ." Moriturus te saluto." reset-term
+            exit
+        then
+
+        repl-buffer @ 0> if
+            0 parse-idx !
+            read
+            eval
+            fg cyan print reset-term
+        then
     again
 ;